Mendelian forms of human genetic disease can be viewed as natural mutagenesis experiments. Over the past decade many disease-causing mutations have been identified through positional cloning: the identification of the causal gene purely on the basis of its genetic location. One unique form of aging, that to date has not been studied at the molecular level, is the Growth retardation, Alopecia, Pseudoanodontia, and Optic atrophy (or GAPO) syndrome. Through extensive clinical efforts and worldwide collaborations we have collected 17 individuals affected with the GAPO progeroid syndrome and identified a genetic locus on Chromosome 2p. We now propose to refine the genetic locus and clone the causal gene or genes as outlined in the following Specific Aims; Aim 1-Refined mapping of the GAPO genetic locus Under the assumption that the GAPO syndrome is a monogenic recessive trait (well supported by all of the available data) we will use homozygosity mapping with lllumina BeadArray technology (the Infinium HumanHap 610K SNP panel) to identify the minimal genetic locus responsible for the syndrome. Aim 2- Identification of the GAPO syndrome gene Using modern approaches to positional cloning, including next generation sequencing, we will screen genes within the final genetic interval for mutations in GAPO syndrome patients. Candidates will be tested in other GAPO patients, in vitro using cell lines from GAPO subjects, and through systematic antisense morpholino knockdown in the zebrafish model. The coexistence of several developmental phenotypes in GAPO syndrome will allow this latter effort. The work we have outlined is designed to identify the causal gene in this unique progeroid syndrome, and will immediately enable the development of in vivo models using mouse knock-in of specific human mutations. The pathways identified will be explored in other forms of human aging, as well as in common disease entities shared with the GAPO syndrome including atherosclerosis, osteoporosis and osteopenia and gonadal failure.